1. Field of the Invention
The present invention relates to a fuel cell stack comprising a plurality of fuel cell units each composed of an electrolyte interposed between an anode electrode and a cathode electrode, the plurality of fuel cell units being stacked with separators intervening therebetween.
2. Description of the Related Art
For example, the solid polymer electrolyte fuel cell comprises a fuel cell unit including an anode electrode and a cathode electrode disposed opposingly on both sides of an electrolyte composed of a polymer ion exchange membrane (cation exchange membrane), the fuel cell unit being interposed between separators. Usually, the fuel cell is used as a fuel cell stack comprising a predetermined number of the fuel cell units and a predetermined number of the separators which are stacked with each other.
In such a fuel cell, a fuel gas such as a gas principally containing hydrogen (hereinafter referred to as xe2x80x9chydrogen-containing gasxe2x80x9d), which is supplied to the anode electrode, is converted into hydrogen ion on the catalyst electrode, and the ion is moved toward the cathode electrode via the electrolyte which is appropriately humidified. The electron, which is generated during this process, is extracted for an external circuit, and the electron is utilized as DC electric energy. An oxygen-containing gas such as a gas principally containing oxygen (hereinafter referred to as xe2x80x9coxygen-containing gasxe2x80x9d) or air is supplied to the cathode electrode. Therefore, the hydrogen ion, the electron, and the oxygen gas are reacted with each other on the cathode electrode, and thus water is produced.
In order to supply the fuel gas and the oxygen-containing gas to the anode electrode and the cathode electrode respectively, a porous layer having conductivity, for example, porous carbon paper is usually disposed on the catalyst electrode layer (electrode surface), and the porous layer is supported by the separator. Further, one or a plurality of gas flow passages designed to have a uniform widthwise dimension are provided on the mutually opposing surfaces of each of the separators.
In such an arrangement, the condensed water or the water produced by the reaction exists in a state of liquid (water) in the gas flow passages. If the water is accumulated in the porous layer, the diffusion performance is lowered concerning the diffusion of the fuel gas and the oxygen-containing gas to the catalyst electrode layer. It is feared that the cell performance is conspicuously deteriorated.
In view of this fact, for example, a solid polymer electrolyte type fuel cell is known, as disclosed in Japanese Laid-Open Patent Publication No. 9-50819, which makes it possible to remove water droplets adhered to the wall surface of the flow passage groove provided on the separator for allowing the fuel gas and the oxygen-containing gas to flow. Specifically, as shown in FIG. 5, the separator 1 comprises through-holes 2a, 2b for the oxygen-containing gas, through-holes 3a, 3b for the heat medium, and through-holes 4a, 4b for the fuel gas which are provided at mutually diagonal positions respectively corresponding to both sides of the catalyst electrode layer.
For example, a plurality of horizontal flow passage grooves 5a and a plurality of vertical flow passage grooves 5b, which make communication between the through-holes 2a, 2b for the oxygen-containing gas, are provided mutually perpendicularly on a first surface 1a of the separator 1 disposed opposingly to the cathode electrode. A plurality of mutually perpendicular grooves are formed on the side of a second surface of the separator 1 in order to make communication between the through-holes 3a, 3b for the heat medium. Similarly, unillustrated grooves, which extend perpendicularly in a meandering manner in the horizontal direction and in the vertical direction respectively, are also formed on the separator 1 disposed opposingly to the anode electrode in order to make communication between the through-holes 4a, 4b for the fuel gas.
When such a fuel cell is used, for example, it is demanded that the fuel cell is carried on a body of an automobile or the like. In this case, it is most practical that the fuel cell is installed under the floor of the automobile. However, if the fuel cell is installed under the floor of the automobile, it is impossible to ensure a sufficient passenger""s space in a vehicle""s cabin, because the height of the automobile is increased, which is not preferred. Therefore, it is necessary that the entire fuel cell is designed to have a low size in the height direction.
However, in the case of the conventional technique described above, the catalyst electrode layer is designed to have a rectangular configuration having a vertical length longer than a horizontal length. Further, the entire separator 1 is constructed to have a substantially square configuration. For this reason, the following problem is pointed out. That is, if it is intended to decrease the size in the height direction of the separator 1, the area of the catalyst electrode layer is considerably decreased. As a result, it is impossible to effectively ensure the electrode area of the stack, and it is difficult to obtain desired power generation performance, especially power generation capacity. In view of this fact, for example, it is conceived that a plurality of fuel cell stacks are arranged in an aligned manner. However, such an arrangement arises other problems in that the structure is complicated, and such an arrangement is not economic.
A principal object of the present invention is to provide a fuel cell stack in which the size in the height direction is effectively suppressed to be low and which makes it possible to reliably obtain desired power generation performance with a simple structure.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.